Prior art motorcycle engines generally include either a dry sump or wet sump lubrication system. In a dry sump lubrication system, the oil is pumped out of the crankcase sump and into an external oil tank or reservoir before the oil is recirculated to the engine. In a wet sump lubrication system, the oil is either slung from the crankcase sump with an oil slinger, or pumped from the crankcase sump to the components of the engine with an oil pump.
One type of oil pump is a gerotor pump, which includes a pump housing and a gerotor positioned within the housing and rotatable relative to the housing. Gerotors generally include a gear having external teeth, and a ring having internal teeth and surrounding the gear. An intake kidney is provided immediately adjacent the gear and ring, allowing oil to be drawn into the gerotor as the gear and ring rotate relative to the pump housing. A discharge kidney is also provided that allows oil to pass out of the gerotor.
Oil is introduced between the ring and the housing to reduce friction as the ring rotates relative to the housing. Although the oil significantly reduces friction between the ring and the housing, a portion of the power driving the ring goes into the shearing of the oil between the ring and the housing.